1. Field of Invention
This invention relates to arrow tips, and more particularly to hunting arrow tips, whose purpose it is to inflect a fatal wound by means of hitting, cutting and penetrating into the desired target game.
2. Prior Art
Over the last few years there has been a trend towards lighter arrows, with a lighter tip. A light weighted tip and arrow results in higher velocities and flatter trajectories during flight. These characteristics make estimating the distance of the desired target, and sighting in said target much less difficult.
Manufacturers have attempted to reduce the weight of their arrow head tips via the thickness and size of the blades, by using lighter construction materials for the tip body, i.e. aluminum, and by reducing the overall size of their tips. Although these modifications have resulted in a substantial weight reduction, at present there are no composite plastic tips on the market.
Because of the aerodynamic geometry of conventional hunting tips, they do not fly true, nor is their flight as predictable as target tips (a bullet shaped tip without fins or blades.) These trajectory variances are a result in part of the aerodynamic drag on the tip. By understanding the components that result in total drag, a design can be made to reduce these effects.
The total aerodynamic drag on an arrow is the summation of three different components i.e. induced drag, wave drag and skin-friction drag. Induced drag is associated with the kinetic energy in the tip vortices which are shed from the blades. Wave drag is a function of the tip and blade profile, and skin-friction drag are the drag forces resulting from pressure stresses acting on the surface of the blade and tip profile (skin-friction drag generally includes shear drag.)
Manufacturers of hunting arrow tips have attempted to design tips that eliminate trajectory variation, and at the same time provide a sufficient blade cut diameter to inflict a fatal wound. However these two parameters are generally conflicting. As the cut diameter increases, trajectory variation increases. In an effort to optimize said parameters, manufacturers have designed vented blades (blades that have a substantial amount of the blade material removed such that the only exposed material is along the blade perimeter) to reduce blade skin-friction drag. The thickness of the blades has also been reduced which in turn reduces the wave drag.
There has been some work to provide an expandable broadhead hunting tip wherein the blades are tucked completely into the body of the tip during flight and are caused to expand upon impact, by means of a point located on the leading end of the tip that slides transversely into the body of the tip (opposite to the flight direction.) The trailing portion of this sliding point consequently forces the blades to expand outward when the tip strikes a target. There are several inherent problems with this design. The design is characterized by a complex geometry that results in increased manufacturing expense and generates higher risk of failure because of failure of the actual tip to meet and comply with specifications in every instance of manufacture. In other words, commercial development of such a tip may easily fall below engineered design criteria because of difficulty of manufacture.
Furthermore, the non-solid point, which slides into the tip body, limits the effectiveness of the hit because the point functions like a shock absorber dissipating some of the tip's energy. In addition, the sliding mechanism in the tip can easily be contaminated with dirt and/or other contaminates causing the siding point to lockup and thus not allow the blades to open.
Finally, the blades are held within the tip body via a rubber band or o-ring. This o-ring can easily be destroyed, upon impact, by the expanding blades, thus rendering the tip useless for repeated shots. Besides these mechanical difficulties, an additional significant problem with the prior art expandable tip is that it is illegal in many States in the United States because in it's closed position, it is less than 0.875 inches in diameter which is the minimum diameter required for hunting tips. Game Wardens measure a tips' diameter when it is in the closed position because if for some reason the tip failed to open it probably would not inflict a fatal wound.
These deficiencies suggest the need for a new arrow tip design which offers both improved performance and enhanced simplicity.